Jetpack Settings: Get rid of "Save Settings" card buttons

"Save Settings" buttons that present for some of the settings cards used only for cards with selects, radio buttons and inputs. All the toggles trigger auto-save on click. I find current Save behavior inconsistent, which is confusing.

I think we can get rid of "Save Settings" buttons altogether, and add auto-save behavior to other control elements (radio buttons, selects, etc)

FWIW the current behavior is similar to Calypso settings. So it might not be an easy task if we still want to maintain the same behavior between wp-admin & Calypso

#### Steps to reproduce the issue

1. Go to Jetpack Settings
2. Find a card with "Save Settings" button
3. Try to make that button become active


Start at the Jetpack Settings cards described in the issue and compare their wp-admin and Calypso behavior. Done means removing all Save Settings buttons and autosaving radio buttons, selects, and inputs while keeping the two settings surfaces consistent.

Written by the indexing model from the issue text.